[ARCMT][NFC] Reduce #include dependencies

Replace some #includes in ARCMigrate source files with more specific includes
and forward declarations. This reduces the number of files that need to be
rebuilt when a header changes (and saves like 1 second of build time). For
example, several files no longer need to be rebuilt when the list of static
analyzer checkers(!) changes.

Differential Revision: https://reviews.llvm.org/D74385

clang/lib/ARCMigrate/ARCMT.cpp

@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "Internals.h"
+#include "clang/ARCMigrate/ARCMT.h"
 #include "clang/AST/ASTConsumer.h"
 #include "clang/Basic/DiagnosticCategories.h"
 #include "clang/Frontend/ASTUnit.h"

clang/lib/ARCMigrate/Internals.h

@@ -9,13 +9,15 @@
 #ifndef LLVM_CLANG_LIB_ARCMIGRATE_INTERNALS_H
 #define LLVM_CLANG_LIB_ARCMIGRATE_INTERNALS_H
 
-#include "clang/ARCMigrate/ARCMT.h"
+#include "clang/Basic/LangOptions.h"
 #include "clang/Basic/Diagnostic.h"
+#include "clang/Frontend/MigratorOptions.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/Optional.h"
 #include <list>
 
 namespace clang {
+  class ASTContext;
   class Sema;
   class Stmt;
 

clang/lib/ARCMigrate/Transforms.cpp

@@ -8,6 +8,7 @@
 
 #include "Transforms.h"
 #include "Internals.h"
+#include "clang/ARCMigrate/ARCMT.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/RecursiveASTVisitor.h"
 #include "clang/Analysis/DomainSpecific/CocoaConventions.h"